Modern science is quantitative, not qualitative. The top breakthroughs in modern science have broken through traditional distinctions of quality or kind. Consider the following:
(1) Newton’s theory of gravitation broke through the traditional distinction between the sublunar and supralunar universe (e.g., the earth and the heavens). All motion is subject to the same laws.
(2) The atomic theory of matter broke through the traditional distinctions between different kinds of matter (e.g., water, earth, air, and fire). All matter is merely a combinations of atoms (or subatomic particles).
(3) Darwin’s theory of evolution broke through the traditional distinctions between different kinds of organisms (e.g., humans and animals). All species are merely variations of life (or genes).
(4) Einstein’s theory of relativity broke through the traditional distinction between space and time. All dimensions are subject to the same laws.
These are breakthroughs in the service of nominalism, which considers distinctions of quality or kind to be merely names and so not essential. As modern science advances, nominalism advances, too. Nominalism is an acid that eats through traditional distinctions of quality and kind (cf. Darwin’s Dangerous Idea by Daniel Dennet).
Modern science is in league with nominalism for at least two reasons: (a) nominalism releases science to develop its own way, unencumbered by traditional distinctions; and (b) modern science follows qualitative parsimony, which prefers the fewest qualitative distinctions, in line with nominalism. The latter principle is known as Occam’s razor, after the arch-nominalist William of Occam (or Ockham).
Realists hold that there are real distinctions of quality and kind and so consider it a loss to eliminate distinctions of quality or kind. While the traditional distinctions may need to be modified, realists hold that distinctions of quality and kind in some form are real.
It is therefore incumbent on realists to reaffirm these distinctions, perhaps with some changes. That puts realism in competition with modern science, even though the actual opponent of realism is nominalism.